The Late-1980 Extratropical Warming of the Northern HemisphereReference
Lo, T.-T. and Hsu, H.-H. 2010. Change in the dominant decadal patterns and the late 1980s abrupt warming in the extratropical Northern Hemisphere. Atmospheric Science Letters11: 210-215.

Background
The authors write that "widespread abrupt warming in the extratropical Northern Hemisphere occurred in the late 1980s," and they say that this warming was associated with a change in the relative influence of a Pacific Decadal Oscillation (PDO)-like pattern and an Arctic Oscillation (AO)-like pattern.

What was done
Utilizing land surface temperature data obtained from the University of East Anglia's Climate Research Unit (Mitchell et al., 2004), plus sea surface temperature data obtained from the UK's Meteorological Office (Rayner et al., 2003), the authors explored the nature of this temperature increase and tested the ability of IPCC/CMIP3 models to simulate it.

What was learned
The two Taiwanese researchers report finding that the emergence of an AO-like pattern in the late 1980s and the concomitant weakening of the previously prevailing PDO-like pattern -- occurring in tandem -- were what led to the "accelerated warming in the Northern Hemisphere." And they say that these results, together with results obtained from current IPCC/CMIP3 models, "do not support the scenario that the emerging influence of the AO-like pattern in the 1980s can be attributed to the anthropogenic greenhouse effect."

What it means
As for other implications of their findings, Lo and Hsu state in their concluding paragraph that "this study indicates the importance of the changing behavior of the decadal fluctuations in the recent climate regime shift," and they highlight what they call "the insufficient capability of the present state-of-the-art IPCC/CMIP3 models in simulating this change."

References
Mitchell, T.D., Carter, T.R., Jones, P.D., Hulme, M. and New, M. 2004. A comprehensive set of high-resolution grids of monthly climate for Europe and the globe: the observed record (1901-2000) and 16 scenarios (2001-2100). Tyndall Centre Working Paper 55, Norwich, United Kingdom.